I looked up what "tar" is. It says that tar is made by distilling coal or Wood. But how could you distill coal or Wood? wouldn't the coal or Wood start to burn if you treat it with high temperatures? And how could you distill tar when it's flammable?
The distillation of tar occurs in an air-tight container, so there is no air to support combustion. The temperatures used are relatively low, so the coal or wood doesn't char so much, but instead does something like melting.